BIO301 Class 8 Flashcards
What is irreversible inhibition?
Occurs when the inhibitor reacts with and COVALENTLY changes the enzyme, killing its activity
What is suicide substrate inhibition?
- special case of irreversible inhibition
- enter the catalytic site & partial catalysis creates an active intermediate that covalently kills the enzyme
3 types of reversible inhibitors
1) competitive
2) uncompetitive
3) mixed & non-competitive
What is competitive inhibition?
A substrate molecule is prevented from binding to the active site of an enzyme by a molecule that is very similar in structure to the substrate
VMAX → unchanged
Km → increased
why?
- you can still reach the same vmax if you flood the system with substrate
- the km is increased because the probability of successful binding decreases
What is mixed/non-competitive inhibition?
Binds either to just the ES complex or just E (that’s why it’s mixed)
VMAX → decreased
Km → unchanged
why?
- vmax decreases because the product formation is lower. Once you inhibit the enzyme or ES complex, you cannot flood with substrate and increase vmax
- Km is unchanged because the binding of inhibition does not decrease probability of binding to the substrate
What is uncompetitive inhibition?
The inhibitor only binds to ES complex which successfully stops the reaction from going forward since it is after the enzyme and substrate bind, it does not affect the substrate binding at all.
VMAX → decreased
Km → decreased
why?
- Km and vmax decreases since product formation is slow or reduced
- Km is reduced because enzyme-substrate is so tightly bound that it is not available to get more substrates
- even if you add more substrates, it is not going to move the reaction forward
- the only way to reverse this is to remove the inhibitor
What is homotropic regulation?
- some regulatory enzymes exhibit cooperativity with small increases in the substrate yielding significant increases in activity
- non-michaelis menten kinetics
- regulated by substrate
What is heterotropic regulation?
- some regulatory enzymes are regulated by negative and/or positive modulators that are different than a substrate
- uses sigmoidal kinetics
Aspartate Transcarbamylase
3 regulators
- homotropic → increase in aspartate & carbamoyl-p causes a T to R state
- positive heterotropic regulation → ATP stimulates ATCase
- negative heterotropic regulation → CTP inhibits ATCase
What is feedback inhibition?
An essential biochemical procedure that makes use of noncompetitive inhibitors to regulate some enzyme reactions
ex) Isoleucine
How is glycogen phosphorylase regulated?
low energy indicated by increased AMP
→ AMP allosterically shifts T to R state
covalent modification (phosphorylation) yields the most active form of the enzyme
Glycagon
hormone secreted by the pancreas when blood glucose levels are LOW → signals low nutritional input (income is low → time to spend savings)
when glucagon is high, insulin is low
Epinephrine (adrenaline)
“fight or flight” hormone; indicates a sudden need for muscle contraction (skeletal muscle, cardiac muscle) and accompanying ATP usage
mobilizes stored glucose in muscle glycogen
insulin
hormone that is secreted by the pancreas when blood glucose levels are HIGH nutritional input (income is high, so time to increase savings)
when insulin is high, glucagon in low
